Exoscopes, endoscopes and other medical instruments can contain image sensors, processors and other circuitry for processing image data and other data, power electronics, light-emitting diodes or other light sources and other heat sources. Normally, the thermal output generated by these heat sources is carried off mainly by natural convection, which is driven by the heating of the air surrounding the medical instrument. The continuing process of miniaturization of electronic components, their increasing performance and their availability at ever lower costs cause that medical instruments contain an increasing number of electronic components with increasing thermal output. Heat dissipation by means of natural convection is therefore no longer sufficient in all cases. A conventional fan or compressor, for forcing convection or a cooling flow of fluid, cannot readily be cleaned and autoclaved and is therefore not considered for use with many medical instruments.